chore: support other git dir for changelogs

make/changelogs.mk

 # from newest to oldest, stop at LAST_RELEVANT_VERSION
-LAST_RELEVANT_VERSION := 1.1.13
+LAST_RELEVANT_VERSION ?= 1.1.13
 # get all versions from shell and drop all that are older than LAST_RELEVANT_VERSION
 # this variable gets expaneded every time it is used, so fetching git tags will change it
 GIT_VERSIONS = HEAD $(shell git tag --sort=-v:refname | awk '1;/$(LAST_RELEVANT_VERSION)/{exit}')
@@ -11,7 +11,7 @@ GIT_VERSION_RANGES = $(join \
 # files that will change if we fetch new tags => if anything is changed,
 # we rebuild all changelogs (in case the history was rewritten somehow)
 # deferred in case we do a fetch first
-GIT_TAG_FILES = $(wildcard .git/refs/tags/*) .git/packed-refs
+GIT_TAG_FILES = $(wildcard $(and $(GIT_DIR),$(GIT_DIR)/).git/refs/tags/*) $(and $(GIT_DIR),$(GIT_DIR)/).git/packed-refs
 VER_CHANGELOGS_MARKDOWN := $(foreach VER,$(GIT_VERSIONS), \
 	$(BUILD_PREFIX)CHANGELOG-$(VER).md)
 VER_CHANGELOGS_HTML := $(foreach VER,$(GIT_VERSIONS), \
@@ -57,7 +57,7 @@ changelog-head-html: $(firstword $(VER_CHANGELOGS_HTML))
 
 $(COMBINED_CHANGELOG_MARKDOWN): $(VER_CHANGELOGS_MARKDOWN)
 # omit unpublished from combined changelog
-	cat $(VER_CHANGELOGS_HTML_IN_COMBINED) > $(COMBINED_CHANGELOG_MARKDOWN)
+	$(if $(strip $(VER_CHANGELOGS_HTML_IN_COMBINED)),cat $(VER_CHANGELOGS_HTML_IN_COMBINED),echo No versions yet) > $(COMBINED_CHANGELOG_MARKDOWN)
 
 GIT_LOG_FORMAT := \#\# %B
 CHANGELOG_VERSION = $(patsubst $(BUILD_PREFIX)CHANGELOG-%.md,%,$@)